Yeah, I agree. I've still got three moubpntain bikes from '08, '09 and they are still in very good shape as life got in the way of riding regularily for the last few years. My brother still rides my old Da Bomb Bouncing Betty from '07 (iirc.) these bikes are a generation old, pre ridiculous geometry, but not vintage. For me, vintage is 20 years old.

Everything is a tradeoff. Usd forks track better, but feel different. Once you get used to the difference, and try to go back to a conventional design, you would wionder how you could have ever ridden a bike with a conventional fork. I could never get used to the feel of the conventional forks after years of MX. The inverted fork switch was revolutionary and dramatically improved the tracking/handling of the bikes. The stiffness at the crown with the larger tubes and greater clamping surface area on the inverted design provides more stable geometry, where conventional forks flex a lot more at the crown with their smaller tubes and smaller clamping area.

Best bang for the buck is the wheels. Most top frames and even many Chinese frames perform well. You will definitely feel a difference in a wheel upgrade before a frame upgrade, with equal amounts being spent on either.

I have been around biking since the early 90's, and the budget solution is opposite of what sells. Build your bike around the best wheels you can get. The wheels are the biggest performance upgrade there is. Suspension design is less important than a good shock and fork. Even a faux bar will work well with a good shock. After that, spend what you can afford.
Really, its almost all about the wheels on a mountain bike.

I've used both and personally like the carbon better. I'm more of a finesse rider than a hack, and the lack of maintenance is a big plus with the carbon. Carbon wheels almost never need truing, if built with proper and even spoke tension. I've had some medical issues this past two years and with my weight up (from medications) to 300lbs, I still haven't broken a carbon product. I'm 6'3" and built like a linebacker. My fit weight is 240-250lbs. If you break carbon, you would have smashed aluminum. For riders in rocky areas, get a rim with a kevlar layer. Amazing impact resistance, or even mix graphite fibres in the resin. Its what boat builders do to improve impact resistance.
On the other hand, I am really liking steel bicycles. With modern butted tubing, weight is about on par with aluminum, with better fatigue resistance than aluminum.